A hybrid vehicle includes an engine and an electric motor and is capable of running by the engine or the electric motor, or is capable of running by the cooperation between the engine and the electric motor. In that case, during the deceleration of the hybrid vehicle, the electric motor is rotated by the turning force of the wheel and functions as an electric generator so that the battery of the hybrid vehicle can be charged (it is referred to as regenerative power generation). When the electric motor performs regenerative power generation, as described above, regeneration torque is generated at the electric motor in proportion to the electric power regenerated by the electric motor. The regeneration torque functions as braking force during the deceleration of the hybrid vehicle (for example, see Patent Literature 1). At that time, for an efficient regenerative power generation by the electric motor, the hybrid vehicle is controlled to disconnect the engine from the electric motor in order to disconnect the engine from the driving system of the hybrid vehicle and eliminate the braking force by the engine brake so that the electric motor can perform regenerative power generation with a maximum regeneration torque (or, namely, a maximum electric power regeneration).
On the other hand, the temperature of the battery increases because chemical reactions are often caused under the condition in which the electric power is often transferred to and from the battery since a nickel hydride battery or the like is used as the battery. It is necessary to perform the regenerative power generation in which the electric power is moderately regenerated under a condition in which the temperature of the battery is high as described above. Then, in that case, such a control is performed as to connect the engine to the electric motor in order to obtain the braking force of the hybrid vehicle as the sum of the braking force by the engine brake and the braking force by the regeneration torque, and in order to keep the electric power regeneration of the electric motor low.